Abnormal spinal stretch reflexes (SSRS) are a major problem for many patients with traumatic brain injury, stroke, cerebral palsy or multiple sclerosis. Spinal hyperreflexia causes postural abnormalities and contractures, and interferes with voluntary movement. Available therapeutic approaches are rarely wholly effective and often ineffective. Operant conditioning can reduce SSRs in non-human primates, and recent studies indicate that it can reduce SSRs in humans also. Thus SSR conditioning could provide a new approach to treating hyperreflexia in humans. The goal of this proposal is to determine whether SSR conditioning can become an effective treatment for hyperreflexia in patients. To achieve this goal, this project will: 1) determine to what extent normal individuals and patients with lesions of specific types can reduce SSRs by operant conditioning; 2) assess how long those reflex changes persist; 3) determine whether reflex changes are accompanied by improvements in function and changes in stiffness about the elbow joint; and 4) define which classes of patients benefit from this new approach. Both normal individuals and hyperreflexive patients will participate. Each will be randomly assigned to the controI group or to the treatment group. Control subjects will have biceps brachii SSRs elicited during a 10-week - extended baseline phase and during a 1-year follow-up phase. Treatment subjects will have a 2-week baseline phase, an 8-week treatment phase, and the same 1 -year follow-up phase as controls. During the treatment phase, SSRs of treatment subjects will be operantly conditioned, i.e., subjects will be rewarded for smaller reflexes. Control subjects will receive no such conditioning, their SSRs will simply be measured. After the treatment group completes the treatment phase and the control group completes the extended baseline, both groups will enter the follow-up phase, which will assess the persistence of reflex change caused by conditioning. In addition, all patient subjects will receive periodic functional evaluations throughout the study to determine whether reflex decrease is associated with functional improvement. This project should determine whether operant conditioning of SSRs can reduce hyperreflexia, reveal whether such reduction is accompanied by persistent functional improvement, and define which patients are most likely to benefit. It may also lead to development of additional conditioning techniques for alleviating other varieties of abnormal CNS function.